<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        * {padding:0px;margin:0px;}
        .box {width:500px;height:180px;overflow: hidden; position: relative;}
        ul {
            list-style:none;
            position: absolute;
            bottom: 10px;
            left: 50%;
            margin-left: -60px;
        }
        ul li {
            float: left;
            width: 10px;
            height:10px;
            background: #fff;
            border-radius: 50%;
            margin-right: 10px;
        }
        ul li.active {background: blue;}
        </style>

</head>
<body>
    <div class="box box1">
        <img src="./imgs/img1.jpg" alt="">
        <ul>
            <li class="active"></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
        </ul>
    </div>
    
    
    <div class="box box2">
        <img src="./imgs/img1.jpg" alt="">
        <ul>
            <li class="active"></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
        </ul>
    </div>

    <div class="box box3">
        <img src="./imgs/img1.jpg" alt="">
        <ul>
            <li class="active"></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
            <li></li>
        </ul>
    </div>

    <script src="./demo.js"></script>
    <script>
        let lbt1 = new Lbt('.box1')
        let lbt2 = new Lbt('.box2')
        let lbt3 = new Lbt('.box3')
    </script>
    
</body>
</html>